Semiconductor method of making electrical connection between an electrically conductive line and a node location, and integrated circuitry

ABSTRACT

A semiconductor processing method of making electrical connection between an electrically conductive line and a node location includes, a) forming an electrically conductive line over a substrate, the substrate having an outwardly exposed silicon containing node location to which electrical connection is to be made, the line having an outer portion and an inner portion, the inner portion laterally extending outward from the outer portion and having an outwardly exposed portion, the inner portion having a terminus adjacent the node location, and b) electrically connecting the extending inner portion with the node location. An integrated circuit is also described. The integrated circuit includes a semiconductor substrate, a node location on the substrate, and a conductive line over the substrate which is in electrical communication with the node location. The conductive line includes an outer portion and an inner portion. The outer portion has a terminus and the inner portion extends laterally away from the outer portion terminus and generally toward the node location. The inner portion is in electrical communication with the node location.

RELATED PATENT DATA

This patent resulted from a continuation application of U.S. patentapplication Ser. No. 09/248,354 filed on Feb. 8, 1999, U.S. Pat. No.6,261,940 B1 which is a continuation of U.S patent application Ser. No.08/699,828 filed on Aug. 20, 1996, U.S. Pat. No. 5,869,391.

TECHNICAL FIELD

This invention relates to an integrated circuit and semiconductorprocessing methods of making electrical connection between anelectrically conductive line and a node location.

BACKGROUND OF THE INVENTION

Single semiconductor devices are grouped into integrated circuits, whichin turn are further densified into large scale integrated semiconductorsystems. The trend in semiconductor integrated circuitry fabricationcontinues to involve a decrease in the size of individual structures.However, this has been accompanied by an increase in the complexity andnumber of such structures aggregated on a single semiconductorintegrated chip.

One type of integrated circuitry comprises memory circuitry. Thisinvention arose out of problems or challenges inherent in producing aparticular type of memory circuitry, namely static random access memory(SRAMs). Such circuitry typically interconnects a gate of one transistordevice to a diffusion area of another transistor device in asemiconductor substrate. One typical prior art method of accomplishingsuch fabrication and interconnection is described with reference toFIGS. 1-4.

FIG. 1 illustrates a semiconductor wafer fragment 10 comprised of a bulksubstrate region 12 and field oxide regions 13. A gate oxide layer 14overlies silicon substrate 12. A polysilicon layer 15 is provided overfield oxide regions 13 and gate oxide layer 14. Such will be utilizedfor fabrication of a transistor gate line of associated SRAM circuitry.A layer 16 of photoresist is provided atop the substrate, and providedwith an opening 17 therein.

Referring to FIG. 2, a contact opening 18 to bulk substrate 12 has beenetched through polysilicon layer 15 and gate oxide layer 14. A desireddiffusion region 20 is provided as shown. Then, the photoresist layer 16of FIG. 1 is stripped.

Referring to FIG. 3, a subsequent polysilicon layer 22 is deposited overfirst polysilicon layer 15 and to within contact opening 18.

Referring to FIG. 4, layers 22 and 15 are patterned and etched toproduce the illustrated transistor gate line 24 which extends over andohmically connects with diffusion region 20.

It would be desirable to improve upon such a construction and method forproducing such a construction. The artisan will also appreciateapplicability of the invention to fabrication of constructions otherthan SRAM circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic sectional view of a prior art semiconductorwafer fragment at one prior art processing step, and is discussed in the“Background” section above.

FIG. 2 is a view of the FIG. 1 prior art wafer fragment at a prior artprocessing step subsequent to that shown by FIG. 1.

FIG. 3 is a view of the FIG. 1 prior art wafer fragment at a prior artprocessing step subsequent to that shown by FIG. 2.

FIG. 4 is a view of the FIG. 1 prior art wafer fragment at a prior artprocessing step subsequent to that shown by FIG. 3.

FIG. 5 is a diagrammatic sectional view of a semiconductor waferfragment at one processing step in accordance with the invention.

FIG. 6 is a view of the FIG. 5 wafer fragment at a processing stepsubsequent to that shown in FIG. 5.

FIG. 7 is a view of the FIG. 5 wafer fragment at a processing stepsubsequent to that shown in FIG. 6.

FIG. 8 is a view of the FIG. 5 wafer fragment at a processing stepsubsequent to that shown in FIG. 7.

FIG. 9 is a view of the FIG. 5 wafer fragment at a processing stepsubsequent to that shown in FIG. 8.

FIG. 10 is a view of the FIG. 5 wafer fragment at a processing stepsubsequent to that shown in FIG. 9.

FIG. 11 is a view of the FIG. 5 wafer fragment at a processing stepsubsequent to that shown in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

In accordance with one aspect of the invention, a semiconductorprocessing method of making electrical connection between anelectrically conductive line and a node location comprises the steps of:

providing a substrate having an outer dielectric surface and a nodelocation to which electrical connection is to be made;

forming a first layer over the outer dielectric surface and the nodelocation;

forming a patterned masking layer over the first layer laterallyadjacent the node location;

forming a second layer over the first layer and the patterned maskinglayer;

patterning and etching the first and second layers and forming anelectrically conductive line therefrom, the second layer of the linehaving a terminus positioned over the patterned masking layer, the firstlayer of the line forming an extension which extends laterally outwardrelative to the second layer terminus; and

electrically connecting the first layer extension with the nodelocation.

In accordance with another aspect of the invention, a semiconductorprocessing method of making electrical connection between anelectrically conductive line and a node location comprises the steps of:

forming an electrically conductive line over a substrate, the substratehaving an outwardly exposed silicon containing node location to whichelectrical connection is to be made, the line having an outer portionand an inner portion, the inner portion laterally extending outward fromthe outer portion and having an outwardly exposed silicon containingportion, the inner portion having a terminus adjacent the node location;

forming a metal layer over the exposed inner portion and the exposednode location; and

exposing the substrate to conditions effective to form an electricallyconductive metal silicide interconnect between the extending innerportion and the node location.

In accordance with another aspect of the invention, an integratedcircuit comprises:

a semiconductor substrate;

a node location on the substrate; and

a conductive line over the substrate in electrical communication withthe node location, the conductive line including an outer portion and aninner portion, the outer portion having a terminus, the inner portionextending laterally away from the outer portion terminus generallytoward and in electrical communication with the node location.

Referring to FIGS. 5-11, and first to FIG. 5, a semiconductor waferfragment in accordance with the invention is indicated generally withreference numeral 25. Such comprises a bulk semiconductor substrate 26(preferably monocrystalline silicon). Other suitable substrate materialsuch as silicon-on-insulator (SOI) may be utilized in connection withthe invention. A field oxide region 28 and gate oxide layers 30 areformed or provided. The field oxide region 28 defines an outerdielectric surface 27 of substrate 26. A node location is indicatedgenerally by reference numeral 32 and defines some location to whichelectrical connection is to be made. A first layer 34 is formed orprovided over the outer dielectric surface and node location, andpreferably comprises conductively doped polysilicon. Preferably, firstlayer 34 is provided to a thickness of around 700 Angstroms, although arange of thicknesses between about 100 Angstroms to 2000 Angstroms wouldsuffice. First layer 34 may be electrically conductive as formed beforea subsequent patterning and etching step, or it may be renderedconductive after provision on dielectric surface 27 as will becomeapparent below. An etch stop or masking layer 36 is formed over firstlayer 34 and overlies field oxide region 28 and gate oxide layers 30. Apreferred material for etch stop layer 36 is a deposited oxide such asSiO₂, and more preferably a TEOS layer having a thickness of about 100Angstroms. However, other thicknesses from between about 20 Angstroms to1000 Angstroms will suffice. Other exemplary materials include nitride,aluminum oxide, TiO_(x), etc.

Referring to FIG. 6, etch stop layer 36 is patterned and etched todefine a patterned etch stop or masking layer (hereinafter designated byreferenced numeral 36) to cover desired substrate active areas and leavedesired substrate field oxide areas exposed. As shown, patterned etchstop layer 36 is positioned proximate, or laterally adjacent nodelocation 32. The etched layer 36 serves as an etch stop for a portion ofthe underlying first layer 34 as will be explained below.

Referring to FIG. 7, a second layer 38 is formed over first layer 34 andthe patterned etch stop layer 36. Preferably, second layer 38 comprisespolysilicon and includes a conductivity enhancing impurity which rendersit electrically conductive immediately upon its formation. Layer 38 ispreferably formed to a thickness of between about 500 Angstroms to10,000 Angstroms. More preferably, layer 38 is formed to a thickness ofbetween about 1000 Angstroms to 2000 Angstroms. Most preferably, layer38 is about 1500 Angstroms thick.

In the preferred embodiment, layers 38 and 34 constitute part of aconductive line and are accordingly electrically conductive. First layer34 can be rendered electrically conductive in a number of ways. Forexample, first layer 34 may be in situ doped with a conductivityenhancing impurity during deposition thereby being electricallyconductive upon its formation. Alternately, it can be doped after itsdeposition. Further, etch stop layer 36 can be doped with a conductivityenhancing impurity, with outdiffusion therefrom rendering first layer 34electrically conductive after provision on the outer dielectric surfaceand node location. Doping layer 36 as just described creates what iscommonly referred to as “doped glass”. Doped glass has an additionaladvantage which stems from its etch rate which is much higher thanthermally grown gate oxide. Thus, it is much more easily removed insubsequent patterning and etching steps described below. Other dopingoptions for first layer 34 include that second layer 38 can be providedwith sufficient conductivity enhancing impurity, such as phosphorus,that outdiffusion therefrom renders first layer 34 electricallyconductive. Further, that portion of first layer 34 which generallyunderlies patterned etch stop layer 36 can be rendered electricallyconductive by lateral diffusion of a conductivity enhancing impurityprovided during a subsequent source/drain implant described below.

Referring to FIGS. 8 and 9, first and second layers 34, 38 are patternedand etched to form an electrically conductive line 40 overlying bulksubstrate 26, field oxide 28, and gate dielectric layer 30. The etchalso further defines node location 32. As shown, line 40 has an outerportion 42 in the form of layer 38, and has an outer portion or secondlayer terminus 44 positioned over etch stop layer 36. Line 40 alsoincludes an inner portion in the form of layer 34 having an extension 46which extends laterally outwardly from outer portion 42 and morespecifically outer portion terminus 44. Inner portion 34 includes aninner portion terminus 48 which is located adjacent node location 32.Inner portion terminus 48 directly overlies gate oxide and hence is notyet electrically connected to or with node location 32.

Referring to FIGS. 8 and 9, an insulating material is deposited andanisotropically etched or overetched to form a sidewall spacer 50 overouter portion terminus 44. Such etch also preferably removes thatportion of gate dielectric layer 30 which overlies node location 32 andwhich is not itself covered by etch stop layer 36 and extension 46. Suchetch outwardly exposes silicon containing node location 32. Preferablyspacer 50 has a lateral width dimension from between around 50 Angstromsto 3000 Angstroms. Even more preferably, spacer 50 has a lateral widthdimension of around 1200 Angstroms. Such overetch is preferablyconducted to a point of removing the exposed portion of etch stop layer36 which is laterally adjacent outer portion terminus 44 and not coveredby sidewall spacer 50. Such overetch exposes at least some of theunderlying inner portion 34/extension 46 as shown. Such may also leave aspacer 45 which is desirably not entirely covering the inner portionterminus 48. Preferably, first layer 34 is of a sufficient thickness(about 700 Angstroms) so that it retains a remnant thickness after theanisotropic etch of around 300 Angstroms to 400 Angstroms. This isbecause the anisotropic etch or overetch typically consumes around 100Angstroms to 300 Angstroms of the first layer. Such thickness isdesirable for providing a sufficient amount of polysilicon for asalicide reaction described below. Additionally, first layer 34 issuitably dimensioned to allow spacer 45 to be formed to a preferredheight on at least a portion thereof. Such preferred spacer height isless than around 100 Angstroms and facilitates formation of a salicidebridge described below in conjunction with FIG. 10.

Referring still to FIGS. 8 and 9, a desired thickness of layer 36 is onewhich blocks the etch of the first and second layers 34, 38 (FIG. 8) sothat the underlying portion of first layer 34 is protected during theetch described in conjunction with FIG. 8. The desired thickness oflayer 36 is also one which minimizes the amount of overetch necessary 8to clear the exposed portion of etch stop layer 36 overlying first layer34 and described in conjunction with FIG. 9. Minimizing the amount ofoveretch required to clear the exposed portion of etch stop layer 36also minimizes or reduces the etch into that portion of oxide layer 28which is not covered. Alternatively, though less preferred, etch stoplayer 36 may be provided in the form of a heavily doped (e.g. phosphorusdoped) PECVD oxide having a high etch rate in HF. If such is the case,then following the first and second layer etch of FIG. 8, a HF dip canbe performed to remove the desired portions of the etch stop layer withminimal effect on the underlying oxide regions or layers. At this point,conductivity enhancing impurity can be provided into substrate 26 toform a source/drain region 33 adjacent inner portion terminus 48. Otheroptions for forming region 33 include providing conductivity enhancingimpurity into the substrate prior to deposition of first layer 34 as bya masked implant step. Alternatively, conductivity enhancing impuritycan be provided into the substrate after deposition of first layer 34but before deposition of etch stop layer 36.

With respect to layers 34 and 38, the sum of the thicknesses of suchlayers is preferably one which provides a stable work function for thedevices. Typically, a thickness of around 800 Angstroms is sufficient.

Referring to FIG. 10, a conductive refractory metal layer 52 is formedover the exposed inner portion 34/extension 46 and the exposed nodelocation 32, as well as outer portion 42 of conductive line 40.Preferably, layer 52 comprises titanium which is formed to a thicknessof between 50 Angstroms and 1000 Angstroms. Even more preferably, layer52 is formed to a thickness of around 200 Angstroms. Metal layer 52 isused to electrically connect, with node location 32, the portion ofinner portion 46 which extends laterally away from outer portionterminus 44. Metals such as nickel, tungsten, platinum, cobalt and otherrefractory metals may also be used to form layer 52.

Referring to FIG. 11, wafer fragment 25, and accordingly metal layer 52(FIG. 10), are heated and accordingly exposed to conditions effective toreact with the exposed silicon areas and form an electrically conductiveinterconnecting silicide bridge 54 between the exposed inner portion34/extension 46 and node location 32. A conventional subsequentselective etch can be used to remove the unreacted metal withoutattacking the silicide. At this point, if the above-referencedsource/drain region was not provided, it could be by provision ofconductivity enhancing impurity into the substrate.

As an alternative to forming a silicide layer 56 atop second layer 38,such layer may be capped with a suitable oxide for insulating it fromthe salicidation process which forms interconnecting silicide bridge 54.

The above-described process essentially provides a conducting line-nodeinterconnecting tongue which extends away from field oxide region 28 andtoward node location 32. The conducting tongue or inner portion 46 is inelectrical communication with node location 32 by virtue of theinterconnecting silicide bridge 54. The conducting tongue forms part ofa conductive line 40 which electrically interconnects node location 32with a gate of another transistor.

Forming a contact between devices as described above eliminatessensitivity to the formation of native oxides over the node location towhich electrical connection is being made. Because of this, higheryields are possible. Additionally, incorporation of the above-describedcontact into SRAM cells provides a smaller cell since the tonguerequires less area than the typical buried contact. This is becauseburied contacts of the prior art utilize an enclosure in polysiliconaround the buried contact which adds to the required area. Further, thetongue may be placed within an alignment tolerance of adjacent gatepolysilicon areas whereas a buried contact must be spaced away by adistance determined by the resolution of the lithography. This istypically a larger distance than the misalignment tolerance.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. A method of making an electrical contact betweenan electrically conductive line and a node location in a semiconductivesubstrate comprising: forming a first dielectric layer over thesemiconductive substrate; forming a first line layer over the firstdielectric layer; forming and patterning a second dielectric layer overthe first line layer, the patterning (1) providing a second dielectriclayer mask over the first line layer and laterally adjacent to a nodelocation, and (2) exposing portions of the first line layer, at leastone exposed portion of the first line layer overlying the node location;forming a second line layer on the exposed portions of the first linelayer, wherein the first and second line layers are in electricalcontact; etching the first and second line layers to form a line, theetching (1) exposing a portion of the second dielectric layer masklaterally adjacent the node location, and (2) defining the line to havean inner portion of the first line layer which extends laterallyrelative to an outer portion of the second line layer; removing portionsof the first dielectric layer overlying the node location effective toexpose the node location; and forming a third conductive layerelectrically connecting the line and the node location.
 2. The method ofclaim 1 wherein the first line layer comprises polysilicon which iselectrically conductive prior to the etching.
 3. The method of claim 1,wherein the first line layer comprises polysilicon which is renderedelectrically conductive after the etching.
 4. The method of claim 3,wherein the first line layer is rendered electrically conductive byforming the second dielectric layer to comprise a conductivity enhancingimpurity and out-diffusing conductivity enhancing impurity from thesecond dielectric layer into the first line layer.
 5. The method ofclaim 1, wherein the second line layer comprises polysiliconconductively doped with a conductivity enhancing impurity, the firstline layer comprises polysilicon and is rendered electrically conductivesubstantially by out-diffusion of conductivity enhancing impurity fromthe second line layer.
 6. The method of claim 1, wherein forming thethird conductive layer comprises forming a refractory metal layer. 7.Themethod of claim 6, further comprising exposing the substrate toconditions effective to form a conductive silicide connecting bridge ofat least some of the refractory metal layer.
 8. A semiconductorprocessing method of making an electrical interconnect between anelectrically conductive line and a substrate node location comprising:forming a first dielectric layer over a substrate, the first dielectriclayer having an outer surface overlying a substrate node location;forming a first line layer overlying the outer dielectric surface andthe substrate node location; forming a second dielectric layer over thefirst line layer and patterning the second dielectric layer to exposeportions of the first line layer, one exposed portion of the first linelayer being adjacent the substrate node location; forming a second linelayer over the first line layer and the patterned second dielectriclayer; etching the first and second line layers to form an interconnectline having an outer portion and an inner portion, and to expose thesubstrate node location, wherein (1) the second line layer comprises theouter portion of the line and has an outer portion terminus disposedover the inner portion, and (2) the first line layer comprises the innerportion of the line and which extends laterally outward relative to theouter portion and having an inner portion terminus adjacent the nodelocation; forming an insulating material over the line and the exposedsubstrate node location; etching the insulating material effective toform a sidewall spacer over at least most of an exposed edge of theouter portion terminus and to remove at least some of the seconddielectric layer over the laterally extending inner portion to expose atleast some of the first line layer; and forming a refractory metal layerover the exposed first line layer and the exposed substrate nodelocation.
 9. The method of claim 8 wherein the first line layercomprises polysilicon which is electrically conductive prior to theetching.
 10. The method of claim 8 wherein the first line layercomprises polysilicon which is rendered electrically conductive afterthe etching.
 11. The method of claim 10 wherein the first line layer isrendered electrically conductive by forming the second dielectric layerto comprise a conductivity enhancing impurity and out-diffusingconductivity enhancing impurity from the second dielectric layer intothe first line layer.
 12. The method of claim 8 wherein the second linelayer comprises polysilicon conductively doped with a conductivityenhancing impurity, the first line layer comprises polysilicon and isrendered electrically conductive substantially by out-diffusion ofconductivity enhancing impurity from the second line layer.